Inhibitors of plasma kallikrein have a number of therapeutic applications, particularly in the treatment of retinal vascular permeability associated with diabetic retinopathy, diabetic macular edema and hereditary angioedema.
Plasma kallikrein is a trypsin-like serine protease that can liberate kinins from kininogens (see K. D. Bhoola et al., “Kallikrein-Kinin Cascade”, Encyclopedia of Respiratory Medicine, p 483-493; J. W. Bryant et al., “Human plasma kallikrein-kinin system: physiological and biochemical parameters” Cardiovascular and haematological agents in medicinal chemistry, 7, p 234-250, 2009; K. D. Bhoola et al., Pharmacological Rev., 1992, 44, 1; and D. J. Campbell, “Towards understanding the kallikrein-kinin system: insights from the measurement of kinin peptides”, Brazilian Journal of Medical and Biological Research 2000, 33, 665-677). It is an essential member of the intrinsic blood coagulation cascade although its role in this cascade does not involve the release of bradykinin or enzymatic cleavage. Plasma prekallikrein is encoded by a single gene and synthesized in the liver. It is secreted by hepatocytes as an inactive plasma prekallikrein that circulates in plasma as a heterodimer complex bound to high molecular weight kininogen which is activated to give the active plasma kallikrein. Kinins are potent mediators of inflammation that act through G protein-coupled receptors and antagonists of kinins (such as bradykinin antagonists) have previously been investigated as potential therapeutic agents for the treatment of a number of disorders (F. Marceau and D. Regoli, Nature Rev., Drug Discovery, 2004, 3, 845-852).
Plasma kallikrein is thought to play a role in a number of inflammatory disorders. The major inhibitor of plasma kallikrein is the serpin C1 esterase inhibitor. Patients who present with a genetic deficiency in C1 esterase inhibitor suffer from hereditary angioedema (HAE) which results in intermittent swelling of face, hands, throat, gastro-intestinal tract and genitals. Blisters formed during acute episodes contain high levels of plasma kallikrein which cleaves high molecular weight kininogen liberating bradykinin leading to increased vascular permeability. Treatment with a large protein plasma kallikrein inhibitor has been shown to effectively treat HAE by preventing the release of bradykinin which causes increased vascular permeability (A. Lehmann “Ecallantide (DX-88), a plasma kallikrein inhibitor for the treatment of hereditary angioedema and the prevention of blood loss in on-pump cardiothoracic surgery” Expert Opin. Biol. Ther. 8, p 1187-99).
The plasma kallikrein-kinin system is abnormally abundant in patients with advanced diabetic macular edema. It has been recently published that plasma kallikrein contributes to retinal vascular dysfunctions in diabetic rats (A. Clermont et al. “Plasma kallikrein mediates retinal vascular dysfunction and induces retinal thickening in diabetic rats” Diabetes, 2011, 60, p 1590-98). Furthermore, administration of the plasma kallikrein inhibitor ASP-440 ameliorated both retinal vascular permeability and retinal blood flow abnormalities in diabetic rats. Therefore a plasma kallikrein inhibitor should have utility as a treatment to reduce retinal vascular permeability associated with diabetic retinopathy and diabetic macular edema.
Plasma kallikrein also plays a role in blood coagulation. The intrinsic coagulation cascade may be activated by factor XII (FXII). Once FXII is activated (to FXIIa), FXIIa triggers fibrin formation through the activation of factor XI (FXI) thus resulting in blood coagulation. Plasma kallikrein is a key component in the intrinsic coagulation cascade because it activates FXII to FXIIa, thus resulting in the activation of the intrinsic coagulation pathway. Furthermore, FXIIa also activates further plasma prekallikrein resulting in plasma kallikrein. This results in positive feedback amplification of the plasma kallikrein system and the intrinsic coagulation pathway (Tanaka et al. (Thrombosis Research 2004, 113, 333-339); Bird et al. (Thrombosis and Haemostasis, 2012, 107, 1141-50).
Contact of FXII in the blood with negatively charged surfaces (such as the surfaces of external pipes or the membrane of the oxygenator that the blood passes during cardiopulmonary bypass surgery) induces a conformational change in zymogen FXII resulting in a small amount of active FXII (FXIIa). The formation of FXIIa triggers the formation of plasma kallikrein resulting in blood coagulation, as described above. Activation of FXII to FXIIa can also occur in the body by contact with negatively charged surfaces on various sources (e.g. bacteria during sepsis, RNA from degrading cells), thus resulting in disseminated intravascular coagulation (Tanaka et al. (Thrombosis Research 2004, 113, 333-339)).
Therefore, inhibition of plasma kallikrein would inhibit the blood coagulation cascade described above, and so would be useful in the treatment of disseminated intravascular coagulation and blood coagulation during cardiopulmonary bypass surgery where blood coagulation is not desired. For example, Katsuura et al. (Thrombosis Research, 1996, 82, 361-368) showed that administration of a plasma kallikrein inhibitor, PKSI-527, for LPS-induced disseminated intravascular coagulation significantly suppressed the decrease in platelet count and fibrinogen level as well as the increase in FDP level which usually occur in disseminated intravascular coagulation. Bird et al. (Thrombosis and Haemostasis, 2012, 107, 1141-50) showed that clotting time increased, and thrombosis was significantly reduced in plasma kallikrein-deficient mice. Revenko et al. (Blood, 2011, 118, 5302-5311) showed that the reduction of plasma prekallikrein levels in mice using antisense oligonucleotide treatment resulted in antithrombotic effects. Tanaka et al. (Thrombosis Research 2004, 113, 333-339) showed that contacting blood with DX-88 (a plasma kallikrein inhibitor) resulted in an increase in activated clotting time (ACT). Lehmann et al. (Expert Opin. Biol. Ther. 2008, 1187-99) showed that Ecallantide (a plasma kallikrein inhibitor) was found to delay contact activated induced coagulation. Lehmann et al. conclude that Ecallantide “had in vitro anticoagulant effects as it inhibited the intrinsic pathway of coagulation by inhibiting plasma kallikrein”.
Plasma kallikrein also plays a role in the inhibition of platelet activation, and therefore the cessation of bleeding. Platelet activation is one of the earliest steps in hemostasis, which leads to platelet plug formation and the rapid cessation of bleeding following damage to blood vessels. At the site of vascular injury, the interaction between the exposed collagen and platelets is critical for the retention and activation of platelets, and the subsequent cessation of bleeding.
Once activated, plasma kallikrein binds to collagen and thereby interferes with collagen-mediated activation of platelets mediated by GPVI receptors (Liu et al. (Nat Med., 2011, 17, 206-210)). As discussed above, plasma kallikrein inhibitors reduce plasma prekallikrein activation by inhibiting plasma kallikrein-mediated activation of factor XII and thereby reducing the positive feedback amplification of the kallikrein system by the contact activation system.
Therefore, inhibition of plasma kallikrein reduces the binding of plasma kallikrein to collagen, thus reducing the interference of plasma kallikrein in the cessation of bleeding. Therefore plasma kallikrein inhibitors would be useful in the treatment of treating cerebral haemorrhage and bleeding from post operative surgery. For example, Liu et al. (Nat Med., 2011, 17, 206-210) demonstrated that systemic administration of a small molecule PK inhibitor, ASP-440, reduced hematoma expansion in rats. Cerebral hematoma may occur following intracerebral haemorrhage and is caused by bleeding from blood vessels into the surrounding brain tissue as a result of vascular injury. Bleeding in the cerebral haemorrhage model reported by Liu et al. was induced by surgical intervention involving an incision in the brain parenchyma that damaged blood vessels. These data demonstrate that plasma kallikrein inhibition reduced bleeding and hematoma volume from post operative surgery. Björkqvist et al. (Thrombosis and Haemostasis, 2013, 110, 399-407) demonstrated that aprotinin (a protein that inhibits serine proteases including plasma kallikrein) may be used to decrease postoperative bleeding.
Other complications of diabetes such as cerebral haemorrhage, nephropathy, cardiomyopathy and neuropathy, all of which have associations with plasma kallikrein may also be considered as targets for a plasma kallikrein inhibitor.
Synthetic and small molecule plasma kallikrein inhibitors have been described previously, for example by Garrett et al. (“Peptide aldehyde . . . ” J. Peptide Res. 52, p 62-71 (1998)), T. Griesbacher et al. (“Involvement of tissue kallikrein but not plasma kallikrein in the development of symptoms mediated by endogenous kinins in acute pancreatitis in rats” British Journal of Pharmacology 137, p 692-700 (2002)), Evans (“Selective dipeptide inhibitors of kallikrein” WO03/076458), Szelke et al. (“Kininogenase inhibitors” WO92/04371), D. M. Evans et al. (Immunolpharmacology, 32, p 115-116 (1996)), Szelke et al. (“Kininogen inhibitors” WO95/07921), Antonsson et al. (“New peptides derivatives” WO94/29335), J. Corte et al. (“Six membered heterocycles useful as serine protease inhibitors” WO2005/123680), J. Stürzbecher et al. (Brazilian J. Med. Biol. Res 27, p 1929-34 (1994)), Kettner et al. (US 5,187,157), N. Teno et al. (Chem. Pharm. Bull. 41, p 1079-1090 (1993)), W. B. Young et al. (“Small molecule inhibitors of plasma kallikrein” Bioorg. Med. Chem. Letts. 16, p 2034-2036 (2006)), Okada et al. (“Development of potent and selective plasmin and plasma kallikrein inhibitors and studies on the structure-activity relationship” Chem. Pharm. Bull. 48, p 1964-72 (2000)), Steinmetzer et al. (“Trypsin-like serine protease inhibitors and their preparation and use” WO08/049595), Zhang et al. (“Discovery of highly potent small molecule kallikrein inhibitors” Medicinal Chemistry 2, p 545-553 (2006)), Sinha et al. (“Inhibitors of plasma kallikrein” WO08/016883), Shigenaga et al. (“Plasma Kallikrein Inhibitors” WO2011/118672), and Kolte et al. (“Biochemical characterization of a novel high-affinity and specific kallikrein inhibitor”, British Journal of Pharmacology (2011), 162(7), 1639-1649). Also, Steinmetzer et al. (“Serine protease inhibitors” WO2012/004678) describes cyclized peptide analogs which are inhibitors of human plasmin and plasma kallikrein.
To date, no small molecule synthetic plasma kallikrein inhibitor has been approved for medical use. Many of the molecules described in the known art suffer from limitations such as poor selectivity over related enzymes such as KLK1, thrombin and other serine proteases, and poor oral availability. The large protein plasma kallikrein inhibitors present risks of anaphylactic reactions, as has been reported for Ecallantide. Thus there remains a need for compounds that selectively inhibit plasma kallikrein, that do not induce anaphylaxis and that are orally available. Furthermore, the vast majority of molecules in the known art feature a highly polar and ionisable guanidine or amidine functionality. It is well known that such functionalities may be limiting to gut permeability and therefore to oral availability. For example, it has been reported by Tamie J. Chilcote and Sukanto Sinha (“ASP-634: An Oral Drug Candidate for Diabetic MacularEdema”, ARVO 2012 May 6th-May 9th, 2012, Fort Lauderdale, Fla., Presentation 2240) that ASP-440, a benzamidine, suffers from poor oral availability. It is further reported that absorption may be improved by creating a prodrug such as ASP-634. However, it is well known that prodrugs can suffer from several drawbacks, for example, poor chemical stability and potential toxicity from the inert carrier or from unexpected metabolites. In another report, indole amides are claimed as compounds that might overcome problems associated with drugs possessing poor or inadequate ADME-tox and physicochemical properties although no inhibition against plasma kallikrein is presented or claimed (Griffioen et al, “Indole amide derivatives and related compounds for use in the treatment of neurodegenerative diseases”, WO2010/142801).
BioCryst Pharmaceuticals Inc. have reported the discovery of the orally available plasma kallikrein inhibitor BCX4161 (“BCX4161, An Oral Kallikrein Inhibitor: Safety and Pharmacokinetic Results Of a Phase 1 Study In Healthy Volunteers”, Journal of Allergy and Clinical Immunology, Volume 133, Issue 2, Supplement, February 2014, page AB39 and “A Simple, Sensitive and Selective Fluorogenic Assay to Monitor Plasma Kallikrein Inhibitory Activity of BCX4161 in Activated Plasma”, Journal of Allergy and Clinical Immunology, Volume 133, Issue 2, Supplement February 2014, page AB40). However, human doses are relatively large, currently being tested in proof of concept studies at doses of 400 mg three times daily.
There are only few reports of plasma kallikrein inhibitors that do not feature guanidine or amidine functionalities. One example is Brandi et al. (“N-((6-amino-pyridin-3-yl)methyl)-heteroaryl-carboxamides as inhibitors of plasma kallikrein” WO2012/017020), which describes compounds that feature an amino-pyridine functionality. Oral efficacy in a rat model is demonstrated at relatively high doses of 30 mg/kg and 100 mg/kg but the pharmacokinetic profile is not reported. Thus it is not yet known whether such compounds will provide sufficient oral availability or efficacy for progression to the clinic. Other examples are Brandi et al. (“Aminopyridine derivatives as plasma kallikrein inhibitors” WO2013/111107) and Flohr et al. (“5-membered heteroarylcarboxamide derivatives as plasma kallikrein inhibitors” WO2013/111108). However, neither of these documents report any in vivo data and therefore it is not yet known whether such compounds will provide sufficient oral availability or efficacy for progression to the clinic. Another example is Allan et al. “Benzylamine derivatives” WO2014/108679.
In the manufacture of pharmaceutical formulations, it is important that the active compound be in a form in which it can be conveniently handled and processed in order to obtain a commercially viable manufacturing process. Accordingly, the chemical stability and the physical stability of the active compound are important factors. The active compound, and formulations containing it, must be capable of being effectively stored over appreciable periods of time, without exhibiting any significant change in the physico-chemical characteristics (e.g. chemical composition, density, hygroscopicity and solubility) of the active compound.
It is known that manufacturing a particular solid-state form of a pharmaceutical ingredient can affect many aspects of its solid state properties and offer advantages in aspects of solubility, dissolution rate, chemical stability, mechanical properties, technical feasibility, processability, pharmacokinetics and bioavailability. Some of these are described in “Handbook of Pharmaceutical Salts; Properties, Selection and Use”, P. Heinrich Stahl, Camille G. Wermuth (Eds.) (Verlag Helvetica Chimica Acta, Zurich). Methods of manufacturing solid-state forms are also described in “Practical Process Research and Development”, Neal G. Anderson (Academic Press, San Diego) and “Polymorphism: In the Pharmaceutical Industry”, Rolf Hilfiker (Ed) (Wiley VCH). Polymorphism in pharmaceutical crystals is described in Byrn (Byrn, S. R., Pfeiffer, R. R., Stowell, J. G., “Solid-State Chemistry of Drugs”, SSCI Inc., West Lafayette, Ind., 1999), Brittain, H. G., “Polymorphism in Pharmaceutical Solids”, Marcel Dekker, Inc., New York, Basel, 1999) or Bernstein (Bernstein, J., “Polymorphism in Molecular Crystals”, Oxford University Press, 2002).
The applicant has developed a novel series of compounds that are inhibitors of plasma kallikrein, which are disclosed in WO2016/083820 (PCT/GB2015/053615). These compounds demonstrate good selectivity for plasma kallikrein and are potentially useful in the treatment of diabetic retinopathy, macular edema and hereditary angioedema. One such compound is N-[(6-cyano-2-fluoro-3-methoxyphenyl)methyl]-3-(methoxymethyl)-1-({4-[(2-oxopyridin-1-yl)methyl]phenyl}methyl)pyrazole-4-carboxamide. Initial attempts to prepare N-[(6-cyano-2-fluoro-3-methoxyphenyl)methyl]-3-(methoxymethyl)-1-({4-[(2-oxopyridin-1-yl)methyl]phenyl}methyl)pyrazole-4-carboxamide yielded a yellow foam. However, the applicant has now developed novel, stable crystalline forms of this compound, which are herein referred to as ‘Form 1’, ‘Form 2’, ‘Form 3’, and ‘Form 4’. The novel solid forms have advantageous physico-chemical properties that render them suitable for development.